Eli linqaku lokuqala kungcelele olunamacandelo amabini. Eli nqaku liza kuqala lixoxe ngembali kunye nemingeni yoyilo lweubushushu obusekwe kwi-thermistoriinkqubo zokulinganisa, kunye nokuthelekiswa kwazo ne-resistance thermometer (RTD) iinkqubo zokulinganisa ubushushu. Kuya kuphinda kuchaze ukukhethwa kwe-thermistor, i-trade-offs ye-configuration, kunye nokubaluleka kwe-sigma-delta analog-to-digital converters (ADCs) kule ndawo yesicelo. Inqaku lesibini liza kuchaza indlela yokwandisa kunye nokuvavanya inkqubo yokugqibela yokulinganisa i-thermistor-based.
Njengoko kuchazwe kuluhlu lwamanqaku angaphambili, Ukuphucula i-RTD ye-Temperature Sensor Systems, i-RTD yinto echasene nokumelana nokushisa. Ii-thermistors zisebenza ngokufanayo kwii-RTDs. Ngokungafaniyo ne-RTDs, ene-coefficient yokushisa efanelekileyo kuphela, i-thermistor ingaba ne-coefficient yokushisa echanekileyo okanye engalunganga. Izifudumezi ze-Negative (NTC) zinciphisa ukuxhathisa kwazo njengoko ubushushu bunyuka, ngelixa izifudumezi ezipholileyo (PTC) zinyusa ukuxhathisa kwazo njengoko ubushushu bunyuka. Kwikhiwane. I-1 ibonisa iimpawu zokuphendula ze-NTC eziqhelekileyo kunye ne-PTC thermistors kwaye ithelekisa kwii-curves ze-RTD.
Ngokubhekiselele kuluhlu lweqondo lokushisa, i-RTD ijika iphantse ibe ngumgca, kwaye inzwa igubungela uluhlu olubanzi lweqondo lokushisa ngaphezu kwe-thermistors (ngokuqhelekileyo -200 ° C ukuya ku-850 ° C) ngenxa yendalo engabonakaliyo (i-exponential) ye-thermistor. Ii-RTDs zidla ngokubonelelwa kwiigophe ezisemgangathweni ezaziwayo, ngelixa iigophe ze-thermistor zihluka ngomenzi. Siza kuxubusha oku ngokubanzi kwicandelo lesikhokelo sokukhethwa kwe-thermistor kweli nqaku.
Ii-thermistors zenziwe ngezinto ezidibeneyo, ngokuqhelekileyo i-ceramics, ii-polymers, okanye i-semiconductors (ngokuqhelekileyo i-oxides yesinyithi) kunye neentsimbi ezicocekileyo (i-platinum, i-nickel, okanye i-copper). I-Thermistors inokubona utshintsho lobushushu ngokukhawuleza kune-RTDs, inika impendulo ngokukhawuleza. Ke ngoko, i-thermistors isetyenziswa ngokuqhelekileyo ngabenzi boluvo kwizicelo ezifuna ixabiso eliphantsi, ubungakanani obuncinci, impendulo ekhawulezayo, ubuntununtunu obuphezulu, kunye noluhlu oluncinci lobushushu, njengolawulo lwe-elektroniki, ulawulo lwendlu kunye nolwakhiwo, iilabhoratri zesayensi, okanye imbuyekezo ebandayo ye-thermocouples kwintengiso. okanye izicelo zoshishino. iinjongo. Usetyenziso.
Kwiimeko ezininzi, izifudumezi ze-NTC zisetyenziselwa umlinganiselo wobushushu obuchanekileyo, hayi izifudumezi ze-PTC. Ezinye ii-thermistors ze-PTC ziyafumaneka ezinokuthi zisetyenziswe kwiisekethe zokukhusela ezidlulayo okanye njenge-fuses eziphinda zisetwe kwizicelo zokhuseleko. Igophe ukumelana-iqondo lobushushu PTC thermistor ibonisa kummandla NTC encinane kakhulu phambi kokuba ufikelele kwindawo yokutshintsha (okanye ingongoma Curie), ngasentla ukuxhathisa inyuka kabukhali imiyalelo eziliqela zobukhulu kuluhlu degrees Celsius. Ngaphantsi kweemeko ezigqithisileyo, i-thermistor ye-PTC iya kuvelisa ukuzifudumeza okuqinileyo xa ubushushu bokutshintsha bugqithiswa, kwaye ukuchasana kwayo kuya kunyuka ngokukhawuleza, okuya kunciphisa igalelo langoku kwinkqubo, ngaloo ndlela ikhusela umonakalo. Indawo yokutshintsha i-PTC thermistors ngokuqhelekileyo iphakathi kwe-60 ° C kunye ne-120 ° C kwaye ayifanelekanga ukulawula imilinganiselo yokushisa kwizicelo ezininzi. Eli nqaku ligxile kwi-thermistors ye-NTC, enokulinganisa okanye ukubeka esweni amaqondo obushushu ukusuka ku -80°C ukuya +150°C. Izifudumezi ze-NTC zinemilinganiselo yokuxhathisa ukusuka kwii-ohm ezimbalwa ukuya kwi-10 MΩ kuma-25°C. Njengoko kubonisiwe kwifig. 1, utshintsho kwiqondo lokunganyangeki ngeqondo likaCelsius kwizifudumezi zibonakala ngakumbi kuneethemometha zokuxhathisa. Xa kuthelekiswa ne-thermistors, uvakalelo oluphezulu lwe-thermistor kunye nexabiso eliphezulu lokumelana lwenza lula ukujikeleza kwayo igalelo, ekubeni i-thermistors ayifuni naluphi na uqwalaselo olukhethekileyo lwe-wiring, njenge-3-wire okanye i-4-wire, ukuhlawulela ukuxhathisa ukukhokela. Uyilo lwe-thermistor lusebenzisa kuphela i-2-wire configuration elula.
Ukuchaneka okuphezulu kwe-thermistor-based based measurement ye-thermistor kufuna ukucutshungulwa kwesignali echanekileyo, ukuguqulwa kwe-analog-to-digital, umgca, kunye nembuyekezo, njengoko kuboniswe kumkhiwane. 2.
Nangona ikhonkco lomqondiso lisenokubonakala lilula, kukho izinto ezininzi ezintsonkothileyo ezichaphazela ubungakanani, iindleko, kunye nokusebenza kwayo yonke ibhodi yomama. Iphothifoliyo ye-ADC echanekileyo ye-ADI ibandakanya izisombululo ezininzi ezidibeneyo, ezifana ne-AD7124-4 / AD7124-8, ebonelela ngenani leenzuzo zoyilo lwenkqubo ye-thermal njengoko uninzi lweebhloko zokwakha ezifunekayo kwisicelo zakhiwe ngaphakathi. Nangona kunjalo, kukho imiceli mngeni eyahlukahlukeneyo ekuyileni nasekuphuculeni izisombululo zomlinganiselo wobushushu obusekwe kwi-thermistor.
Eli nqaku lixoxa ngale miba nganye kwaye libonelela ngeengcebiso zokuzisombulula kunye nokwenza lula ngakumbi inkqubo yoyilo lweenkqubo ezinjalo.
Kukho iintlobo ngeentlobo zeNTC thermitorskwimarike namhlanje, ngoko ke ukukhetha thermistor elungileyo isicelo sakho kunokuba ngumsebenzi onzima. Qaphela ukuba i-thermistors zidweliswe ngexabiso lazo eliqhelekileyo, elithetha ukuchasana kwazo kwi-25 ° C. Ngoko ke, i-thermistor ye-10 kΩ inokumelana okuqhelekileyo kwe-10 kΩ kwi-25 ° C. Izifudumezi zinexabiso eliqhelekileyo okanye elisisiseko lokuxhathisa ukusuka kwii-ohm ezimbalwa ukuya kwi-10 MΩ. Izifudumezi ezinemilinganiselo ephantsi yokuxhathisa (ukumelana negama le-10 kΩ okanye ngaphantsi) ngokuqhelekileyo zixhasa amaqondo obushushu asezantsi, afana no -50°C ukuya +70°C. Izifudumezi ezinemilinganiselo ephezulu yokuxhathisa zinokumelana namaqondo obushushu ukuya kuma 300°C.
Isixhobo se-thermistor senziwe nge-oxide yensimbi. I-Thermistors ifumaneka ngebhola, i-radial kunye neemilo ze-SMD. Amaso e-Thermistor afakwe kwi-epoxy coated okanye iglasi egqunywe ukhuseleko olongezelelweyo. I-epoxy coated ball thermistors, i-radial kunye ne-surface thermistors zifanelekile kumaqondo obushushu ukuya kwi-150 ° C. Izifudumezi zeglasi zeglasi zilungele ukulinganisa amaqondo obushushu aphezulu. Zonke iintlobo zeengubo / ukupakishwa zikwakhusela ngokuchasene nokuhlwa. Ezinye i-thermistors ziya kuba nezindlu ezongezelelweyo zokukhusela okongeziweyo kwiindawo ezinzima. Ii-thermistors ze-Bead zinexesha lokuphendula ngokukhawuleza kune-radial / SMD thermistors. Nangona kunjalo, azihlali ixesha elide. Ngoko ke, uhlobo lwe-thermistor olusetyenzisiweyo luxhomekeke kwisicelo sokugqibela kunye nokusingqongileyo apho i-thermistor ikhona. Uzinzo lwexesha elide lwe-thermistor luxhomekeke kwizinto zayo, ukupakishwa kunye noyilo. Ngokomzekelo, i-epoxy-coated NTC thermistor inokutshintsha i-0.2 ° C ngonyaka, ngelixa i-thermistor evaliweyo itshintsha kuphela i-0.02 ° C ngonyaka.
Ii-thermitors ziza ngokuchaneka okwahlukileyo. Izifudumezi ezisemgangathweni ngokuqhelekileyo zinokuchaneka kwe-0.5°C ukuya kwi-1.5°C. Ukulinganiswa kokumelana ne-thermistor kunye nexabiso le-beta (umlinganiselo we-25 ° C ukuya ku-50 ° C / 85 ° C) unokunyamezela. Qaphela ukuba ixabiso le-beta ye-thermistor liyahluka ngokomenzi. Umzekelo, i-10 kΩ izifudumezi ze-NTC ezivela kubavelisi abohlukeneyo ziya kuba namaxabiso ahlukeneyo e-beta. Kwiisistim ezichaneke ngakumbi, iithermistors ezifana ne-Omega™ 44xxx series zingasetyenziswa. Zinokuchaneka kwe-0.1°C okanye i-0.2°C ngaphezu kobushushu obuphakathi kwe-0°C ukuya kuma-70°C. Ngoko ke, uluhlu lwamaqondo okushisa anokulinganiswa kunye nokuchaneka okufunekayo phezu kolu luhlu lweqondo lokushisa lugqiba ukuba ngaba i-thermistors ifanelekile kwesi sicelo. Nceda uqaphele ukuba phezulu ukuchaneka kwe-Omega 44xxx series, indleko ephezulu.
Ukuguqula ukuxhathisa kwidigri zeCelsius, ixabiso le-beta lidla ngokusetyenziswa. Ixabiso le-beta lichongwa ngokwazi amanqaku amabini okushisa kunye nokuchasana okuhambelanayo kwindawo nganye yokushisa.
I-RT1 = Ukumelana nobushushu 1 RT2 = Ukumelana nobushushu 2 T1 = Ubushushu 1 (K) T2 = Ubushushu 2 (K)
Umsebenzisi usebenzisa ixabiso le-beta elikufutshane kuluhlu lobushushu obusetyenziswa kwiprojekthi. Uninzi lweenkcukacha zethermistor zidwelisa ixabiso le-beta kunye nonyamezelo lwe-25°C kunye nokunyamezelwa kwexabiso le-beta.
Izifudumezi ezichanekileyo eziphezulu kunye nezisombululo ezichanekileyo eziphezulu zokuphelisa ezifana ne-Omega 44xxx series zisebenzisa i-equation ye-Steinhart-Hart ukuguqula ukuchasana kwi-degrees Celsius. I-Equation 2 ifuna i-constants ezintathu A, B, kunye no-C, zinikwe kwakhona ngumenzi wenzwa. Ngenxa yokuba i-equation coefficients iveliswa kusetyenziswa amanqaku amathathu obushushu, i-equation ephumayo inciphisa impazamo evezwe ngomgca (ngokuqhelekileyo i-0.02 ° C).
I-A, B kunye no-C zii-constants ezithathwe kwiindawo ezintathu zokubeka ubushushu. R = ukumelana ne-thermistor kwi-ohms T = iqondo lokushisa kwii-K degrees
Kwikhiwane. I-3 ibonisa uchulumanco lwangoku lwenzwa. I-Drive yangoku isetyenziswe kwi-thermistor kwaye i-current efanayo isetyenziswe kwi-resistor echanekileyo; isixhasi esichanekileyo sisetyenziswa njengesalathiso sokulinganisa. Ixabiso le-reference resistor kufuneka libe likhulu okanye lilingane nexabiso eliphezulu lokumelana ne-thermistor (kuxhomekeke kwiqondo lokushisa eliphantsi elilinganiswe kwinkqubo).
Xa ukhetha i-excitation current, ukuchasana okuphezulu kwe-thermistor kufuneka kwakhona kuthathelwe ingqalelo. Oku kuqinisekisa ukuba i-voltage kwi-sensor kunye ne-reference resistor ihlala ikwinqanaba elamkelekileyo kwi-electronics. Indawo yangoku yomthombo ifuna i-headroom okanye imveliso ehambelanayo. Ukuba i-thermistor inokumelana okuphezulu kwiqondo lokushisa elisezantsi elinokulinganiswa, oku kuya kubangela umbane ophantsi kakhulu. Ngoko ke, i-voltage eveliswa kwi-thermistor kwiqondo lokushisa eliphezulu incinci. Amanqanaba okuzuza acwangcisiweyo angasetyenziselwa ukwandisa umlinganiselo wale miqondiso yomgangatho ophantsi. Nangona kunjalo, inzuzo kufuneka icwangciswe ngokuguquguqukayo kuba inqanaba lomqondiso ukusuka kwi-thermistor liyahluka kakhulu ngeqondo lokushisa.
Enye inketho kukuseta inzuzo kodwa usebenzise i-dynamic drive yangoku. Ke ngoko, njengoko inqanaba lesiginali ukusuka kwi-thermistor litshintsha, ixabiso langoku lokuqhuba litshintsha ngamandla ukuze i-voltage ephuhliswe kwi-thermistor ingaphakathi koluhlu oluchaziweyo lwesixhobo sombane. Umsebenzisi kufuneka aqinisekise ukuba umbane ophuhliswe kwireferensi yereferensi ukwakwinqanaba elamkelekileyo kwizinto zombane. Zombini iinketho zifuna umgangatho ophezulu wokulawula, ukubeka iliso rhoqo kwi-voltage kwi-thermistor ukwenzela ukuba i-electronics inokulinganisa umqondiso. Ngaba kukho inketho elula? Cinga ngokuvuselela amandla ombane.
Xa i-voltage ye-DC isetyenziswe kwi-thermistor, okwangoku ngokusebenzisa i-thermistor ngokuzenzekelayo izikali njengoko utshintsho lwe-thermistor lutshintsha. Ngoku, usebenzisa i-resistor yokulinganisa ngokuchanekileyo endaweni ye-reference resistor, injongo yayo kukubala i-current flowing through the thermistor, ngaloo ndlela ivumela ukuchasana kwe-thermistor ukuba kubalwe. Ekubeni i-voltage ye-drive isetyenziswa njengomqondiso wesalathiso we-ADC, akukho nqanaba lokuzuza elifunekayo. Iprosesa ayinayo umsebenzi wokubeka iliso kwi-voltage ye-thermistor, imisela ukuba inqanaba lesignali linokulinganiswa nge-electronics, kunye nokubala ukuba yiyiphi inzuzo ye-drive / ixabiso langoku lifuna ukulungiswa. Le yindlela esetyenziswe kweli nqaku.
Ukuba i-thermistor inomlinganiselo omncinci wokumelana kunye noluhlu lokumelana, i-voltage okanye i-excitation yangoku ingasetyenziswa. Kule meko, i-drive current kunye nenzuzo inokulungiswa. Ngaloo ndlela, isiphaluka siya kuba njengoko kuboniswe kuMzobo 3. Le ndlela ifanelekile kuba iyakwazi ukulawula i-current ngokusebenzisa i-sensor kunye ne-resistor yereferensi, exabisekileyo kwizicelo zamandla aphantsi. Ukongezelela, ukuzifudumeza kwe-thermistor kuyancitshiswa.
I-voltage excitation ingasetyenziselwa i-thermistors enemilinganiselo ephantsi yokumelana. Nangona kunjalo, umsebenzisi kufuneka ahlale eqinisekisa ukuba okwangoku ngokusebenzisa inzwa ayikho phezulu kakhulu kwinzwa okanye isicelo.
I-voltage excitation yenza lula ukuphunyezwa xa usebenzisa i-thermistor enezinga elikhulu lokumelana kunye noluhlu olubanzi lobushushu. Ukuchasana okukhudlwana okuqhelekileyo kunika inqanaba elamkelekileyo lokulinganiswa kwangoku. Nangona kunjalo, abaqulunqi kufuneka baqinisekise ukuba ikhoyo ngoku ikwinqanaba elamkelekileyo phezu komgangatho wokushisa oxhaswa sisicelo.
I-Sigma-Delta ADCs inikezela ngeenzuzo ezininzi xa uyila inkqubo yokulinganisa i-thermistor. Okokuqala, ngenxa yokuba i-sigma-delta ye-ADC iphinda iphinde ifake igalelo le-analog, ukuhluzwa kwangaphandle kugcinwa kuncinci kwaye imfuno yodwa yi-RC elula yokucoca. Babonelela ngokuguquguquka kohlobo lokucoca kunye nesantya se-baud yemveliso. Uhluzo lwedijithali olwakhelwe ngaphakathi lunokusetyenziswa ukucinezela naluphi na uphazamiseko kwizixhobo ezisebenza ngamandla. Izixhobo ze-24-bit ezifana ne-AD7124-4/AD7124-8 zinesisombululo esipheleleyo ukuya kuthi ga kwi-21.7 bits, ngoko ke zibonelela ngesisombululo esiphezulu.
Ukusetyenziswa kwe-sigma-delta ADC ilula kakhulu ukuyila kwe-thermistor ngelixa inciphisa ukucaciswa, iindleko zenkqubo, indawo yebhodi, kunye nexesha lokuthengisa.
Eli nqaku lisebenzisa i-AD7124-4/AD7124-8 njenge-ADC ngenxa yokuba isandi esiphantsi, i-low current, i-ADC echanekileyo ene-PGA eyakhelwe-ngaphakathi, ireferensi eyakhelwe-ngaphakathi, igalelo le-analog, kunye ne-reference buffer.
Nokuba usebenzisa i-drive yangoku okanye i-voltage ye-drive, ulungelelwaniso lwe-ratiometric luyacetyiswa apho i-voltage yereferensi kunye ne-sensor voltage ivela kumthombo ofanayo wokuqhuba. Oku kuthetha ukuba naluphi na utshintsho kumthombo wokuvuselela aluyi kuchaphazela ukuchaneka komlinganiselo.
Kwikhiwane. I-5 ibonisa ukuhamba ngokuqhubekayo kwi-thermistor kunye nokuchaneka kwe-resistor RREF, i-voltage ephuhliswe kwi-RREF yi-voltage yereferensi yokulinganisa i-thermistor.
Intsimi yangoku ayifuni ukuba ichanekile kwaye ingazinzanga njengoko naziphi na iimpazamo kwintsimi yangoku ziya kupheliswa kolu qwalaselo. Ngokubanzi, uvuselelo lwangoku lukhethwa ngaphezu kokuvuswa kwamandla ombane ngenxa yolawulo oluphezulu lobuntununtunu kunye nokhuseleko olungcono lwengxolo xa inzwa ibekwe kwiindawo ezikude. Olu hlobo lwendlela ye-bias idla ngokusetyenziselwa ii-RTDs okanye ii-thermistors ezinamaxabiso aphantsi okumelana. Nangona kunjalo, kwi-thermistor enexabiso eliphezulu lokuchasana kunye novakalelo oluphezulu, inqanaba lesignali eliveliswa lutshintsho lweqondo lokushisa ngalinye liya kuba likhulu, ngoko ke i-voltage excitation isetyenziswa. Umzekelo, i-10 kΩ thermistor inokumelana ne-10 kΩ kwi-25 ° C. Kwi-50 ° C, ukuchasana kwe-NTC thermistor yi-441.117 kΩ. Ubuncinci bokuqhuba ngoku obuyi-50 µA obubonelelwa yi-AD7124-4/AD7124-8 yenza i-441.117 kΩ × 50 µA = 22 V, ephakame kakhulu kwaye ingaphandle koluhlu olusebenzayo lwee-ADC ezininzi ezikhoyo ezisetyenziswa kule ndawo yesicelo. Ii-thermistors zihlala ziqhagamshelwe okanye zibekwe kufutshane ne-elektroniki, ngoko ke ukunganyangeki ekuqhubeni ngoku akuyomfuneko.
Ukongeza i-resistor yoluvo kuthotho njengesekethe ye-voltage yesahluli iya kumda okwangoku nge-thermistor ukuya kwixabiso layo elincinci lokumelana. Kolu lungelelwaniso, ixabiso le-resistor yoluvo RSENSE kufuneka lilingane nexabiso lokumelana ne-thermistor kwiqondo lobushushu lereferensi ye-25 ° C, ukuze amandla ombane ophumayo alingane nendawo ephakathi yombane wereferensi kwiqondo lobushushu eliqhelekileyo 25 ° CC Ngokufanayo, ukuba i-thermistor ye-10 kΩ ene-resistance ye-10 kΩ kwi-25 ° C isetyenziswa, i-RSENSE kufuneka ibe yi-10. kΩ. Njengoko iqondo lobushushu litshintsha, ukuxhathisa kwe-thermistor ye-NTC nako kuyatshintsha, kwaye umlinganiselo we-voltage ye-drive kwi-thermistor nayo iyatshintsha, ikhokelela ekubeni amandla ombane aphumayo alingane nokumelana ne-NTC thermistor.
Ukuba ireferensi yombane ekhethiweyo esetyenziselwa ukunika amandla i-thermistor kunye / okanye i-RSENSE ihambelana nombane wesalathiso we-ADC osetyenziselwa ukulinganisa, inkqubo imiselwe kumlinganiselo we-ratiometric (Umfanekiso 7) ukwenzela ukuba nayiphi na impazamo enxulumene nomthombo wombane iya kuba calanye ukuyisusa.
Qaphela ukuba mhlawumbi i-resistor yoluvo (i-voltage driven) okanye i-reference resistor (i-current driven) kufuneka ibe nonyamezelo oluphantsi lokuqala kunye ne-low drift, njengoko zombini iinguqu zinokuchaphazela ukuchaneka kwenkqubo yonke.
Xa usebenzisa i-thermistors ezininzi, i-voltage yokuvuselela enye ingasetyenziswa. Nangona kunjalo, i-thermistor nganye kufuneka ibe ne-resistor yayo echanekileyo, njengoko kubonisiwe kwifig. 8. Enye inketho kukusebenzisa i-multiplexer yangaphandle okanye i-low-resistance switch kwi-state, evumela ukwabelana nge-resistor enye echanekileyo. Ngolu lungelelwaniso, i-thermistor nganye idinga ixesha lokumisa xa ilinganisiwe.
Isishwankathelo, xa uyila inkqubo yokulinganisa ubushushu obusekelwe kwi-thermistor, kukho imibuzo emininzi ekufuneka iqwalaselwe: ukukhethwa kwenzwa, i-sensor wiring, i-component selection-trade-offs, ukucwangciswa kwe-ADC, kunye nendlela ezi ziguquko ezahlukeneyo ezichaphazela ngayo ukuchaneka ngokubanzi kwenkqubo. Inqaku elilandelayo kolu ngcelele lichaza indlela yokuphucula uyilo lwenkqubo yakho kunye nohlahlo lwabiwo-mali lwempazamo yenkqubo ukufezekisa umsebenzi ojolise kuwo.
Ixesha lokuposa: Sep-30-2022